The present invention is in sharp contrast to the traditional wheeled vehicle steering system. The structure, adjustment, and alignment of the steering mechanism of a wheeled vehicle is a somewhat complicated matter involving various relationships of each steerable wheel axle to the vehicle body referred to as caster, camber, toe-in, Ackerman angle and the like. No attempt is made here to present a detailed discussion of all of these factors, except as they relate to the improvements of the present invention.
For many decades the steering system for automotive vehicles has utilized a front axle which does not rotate about a vertical axis when the vehicle is steered to the right or the left. Rather, each front wheel is provided with a stub axle which is rotatable about a vertically disposed king-pin. Accordingly, it is necessary to provide means by which the front wheels turn to the left or turn to the right together in a coordinated fashion. It was long ago determined that optimum steering was not achieved with strictly parallel motion of the front wheels because the outwardly turning wheel is closer to the vehicle turning center than the inwardly turning wheel and needs to rotate through a greater angle. This refinement and provision for steering control is referred to as the Ackerman angle provision.
A common and conventional wheeled vehicle steering system provides for the rotation of the steering column or steering shaft to be converted into linear motion of a link which imparts a rotating motion to the stub axle of the wheel through a steering control arm extending from the stub axle. The common means for providing coordinated motion of the two steerable wheels includes a track arm which also is fixed with respect to the stub axle on each wheel together with a track rod extending between the two track arms so that the two front wheels are constrained to move in a predetermined relationship either to the right or to the left. In most cases the linkage provided does not maintain the wheels parallel but rather provides a nonlinear turning relationship which takes into account the Ackerman angle provision.
Hydraulic systems have been incorporated in conjunction with wheeled vehicle steering systems and perhaps the most common form of such hydraulic system is a power assist for the steering shaft which retains the above discussed track rod and track arm arrangement for coordinating turning motion of the steerable wheels. As mentioned above, the present invention eliminates reliance upon a track rod or other direct mechanical linkage between the left and right steerable wheels by causing the turning motion of each wheel to be effected by its own independent hydraulic actuator having no operative connection back to the vehicle body other than that provided by hydraulic hoses.
Steering systems for wheeled vehicles have been proposed in prior patents which employ hydraulic cylinders, but any of the known steering systems employing hydraulic cylinders have been unable to provide positive coordination (i.e. not implemented with a servomotor) between left and right steered wheels through hydraulic cylinder motion alone without providing a direct mechanical connection between the left side and the right side wheel.
U.S. Pat. No. 5,094,312 to Hakel dated Mar. 10, 1992 (U.S. CL. 180/132) shows a vehicle steering system in which the left and right steering control arms for the front wheels are both operated by a single double-acting hydraulic piston with oppositely directed piston rods each coupled by a mechanical link to a respective steering control arm. This single piston arrangement is in effect a direct mechanical linkage from the left side wheel to the right side wheel and there are not two independent hydraulic cylinders for the respective left and right steerable wheels. U.S. Pat. No. 4,986,387 to Thompson et al., dated Jan. 2, 1991 (U.S. CL. 180/212) shows a steerable wheeled vehicle with a steerable wheel for which turning motion is provided by hydraulic cylinder and a rack and pinion, but since there is only one steerable wheel, it provides no teaching with respect to coordination of two steerable wheels relevant to the present invention.
U.S. Pat. No. 5,090,512 to Mullet et al., dated Feb. 25, 1992 (U.S. CL. 180/236), like the patent to Hakel, relies on a direct mechanical connection from the left side to the right side of the steering system including a rotatable shaft and cam pulleys operating a cable arrangement for wheel steering. U.S. Pat. No. 4,006,664 to Brown has hydraulic operated steering, but like the patent to Hakel has only a single cylinder for left and right wheels, the coordinated motion of which must be provided by a linkage connecting left and right wheels with the single cylinder provided for their operation.
In addition to providing the features and advantages described, above, it is an object of the present invention to provide a, wheeled vehicle steering system which achieves coordination between the steering motion of the left and right wheels by providing independently controlled hydraulic actuators, the motions of which are coordinated through the hydraulic systems thereof, thereby avoiding the necessity of direct mechanical linkage extending between the right side and left side wheels of the vehicle.
It is another object of the present invention to provide a pair of left side hydraulic cylinders and a pair of right side hydraulic cylinders for a steerable wheeled vehicle wherein one cylinder of each pair is positioned at a steerable wheel and the other cylinder of each pair is positioned in proximity to the steering wheel or other steering control device and coupled thereto, thereby eliminating the necessity for a conventional elongated steering column extending from the driver position to the lower front portion of the vehicle.
It is yet another object of the present invention to provide a steering system for a wheeled vehicle wherein steering motion of each of the steerable wheels is provided by a hydraulic actuator positioned near or at such wheel together with means remote from the steerable wheels for coordinating the motion of the hydraulic actuators and obviating the necessity for a direct mechanical linkage between the left steerable wheel and the right steerable wheel.
It is still another object of the present invention to provide a steering system for a wheeled vehicle with at least two independently suspended steerable wheels in which the steerable wheels are each provided with a hydraulic actuator for producing steering motion for the wheel, and such hydraulic actuator is mounted with respect to the independent suspension for the wheel to allow large-angle vertical motion of the wheel suspension with turning forces provided to the wheel through flexible hydraulic hose connections from the vehicle body to the suspension-mounted hydraulic actuators.